Tobacco Seed size
Tobacco seed is nearly as fine as mustard seed. One - twentieth of an ounce is more than sufficient to produce plants for one acre; that is to say, enough seed to cover a coin the size of 1 pence (UK) or a 5 cent coin (EURO) or 1 cent (USA).
I don’t have other coins for comparison but I guess that if you have read this far you can find this out.
Opening the seeds
When you first open your seeds it is best to do this carefully onto a piece of white paper.
I have found that making a crease in the paper beforehand allows for easy pouring if you want to place the grains in another container.
If you are getting the seeds straight from a tobacco pod this is definitely useful.
if you are opening seeds from a pod gently pull apart the side away from the stalk over the paper and with a little persuasion the tiny seeds will pour straight out.
To store them you can put them in a seed envelope or tiny jar.
They should keep for about 2 years in this state. I have not tried to germinate seeds older than this so they may keep even longer.